1. Field of the Invention
The present invention relates to a sidelight-type spread illuminating apparatus including a light guide plate in which light sources are arranged at an incident light end surface for emitting widely spread light from emitting portions.
2. Description of the Related Art
As an illumination unit in a liquid crystal display panel, a sidelight-type spread illuminating apparatus (backlight) in which an LED, which is compact and has superior environmental compatibility, is arranged along a side end surface of a light guide plate, has been widely used mainly in the fields of compact portable information devices such as mobile phones and the like. Recently, in order to accommodate even thinner compact portable information devices, light guide plates in which an inclined part that tapers in thickness away from the side end surface (hereinafter, also referred to as the incident light surface) at which the LED is arranged is formed between the incident light surface and an emitting portion are being used. The use of such a light guide plate allows the emitting portion of the light guide plate to be formed thinner regardless of the thickness of the LED.
In this type of spread illuminating apparatus, an LED is normally arranged opposing the incident light surface of the light guide plate in a state that it is mounted on a strip-shaped circuit board. In this configuration, the front portion of the circuit board is tightly fixed to a portion of the light guide plate (including an inclined surface of the inclined part) near the incident light surface to fix the positioning of the LED relative to the light guide plate.
Conventionally, in this kind of spread illuminating apparatus, when light which has been emitted from the LED and entered into the light guide plate is reflected on the inclined surface, it is absorbed by the circuit board tightly fixed to the inclined surface. Further, a light-emitting surface of the LED cannot be faced in parallel to the incident light surface of the light guide plate in a state that the circuit board is tightly fixed to the inclined surface of the light guide plate. Therefore, there has been a problem in that a portion of the light which has been emitted from the light-emitting surface of the LED leaks to the outside without entering the incident light surface of the light guide plate, and this causes a decrease in the brightness of the illumination light.
Thus, in order to solve the above-described problem and increase the brightness of the illumination light, the present applicants first proposed the following spread illuminating apparatus (refer to Japanese Patent Application Laid-Open (JP-A) No. 2011-96523).
FIG. 5 is a cross-section view schematically illustrating the overall structure of a spread illuminating apparatus showing one example given in JP-A 2011-96523. In the spread illuminating apparatus 100 shown in FIG. 5, a light guide plate 121 includes an incident light part 126 formed in front of an incident light surface 122, an inclined part 127 that is formed continuously with the incident light part 126 and tapers in thickness toward the forward direction, and an emitting portion 128 that is formed in front of the inclined part 127 and emits from an emitting surface 125 light from an LED 111 guided through the inclined part 127. A pedestal 129 for fixing an FPC 131 is formed in a region excluding a portion in front of the LED 111 of an inclined surface 127a of the inclined part 127 formed near the incident light surface 122 of the light guide plate 121 so that a principal flat surface 129a of the pedestal 129 is approximately orthogonal to the incident light surface 122 of the light guide plate 121.
In the spread illuminating apparatus 100, according to the above-described structure, a light-emitting surface 112 of the LED 111 faces approximately in parallel the incident light surface 122 of the light guide plate 121 in a state that the FPC 131 is fixed to the pedestal 129. Therefore, light which has been emitted from the light-emitting surface 112 of the LED 111 can be efficiently introduced into the light guide plate 121 without any light leakage. In this way, the spread illuminating apparatus 100 solves the above-described problem and achieves an increase in the brightness of the illumination light.
Further, in the spread illuminating apparatus 100, in a state that the FPC 131 is fixed to the pedestal 129, a gap is formed between the inclined surface 127a at the portion in front of the LED 111 and a surface 131a of the FPC 131 on the side that opposes the inclined surface 127a. Therefore, an effect is obtained by which light entering into the light guide plate 121 and is reflected on the inclined surface 127a is prevented from being absorbed by the FPC 131, thereby achieving an increase in the brightness of the illumination light.